The gargantuan blob of light Louisiana crude floating in the Gulf of Mexico has already closed oyster beds, shut down shrimpers, cancelled fishing tournaments and panicked beach hoteliers from New Orleans to Key West.

With the vast majority of the oil floating offshore, where it will land and whom it will affect have become a guessing game fraught with worry. Wherever the oil goes, it threatens to obliterate billions of dollars for the region's tourism and fishing industries.

"It's like waiting for a hurricane to hit," said Mike Voisin, owner of Motivatit Seafood, which harvests oysters from the gulf. "We don't know where it will go. Every day we look at the forecasting maps."

"We're praying hard," said Ed Schroeder, director of the tourist bureau in Pensacola Bay, Fla., where people are wishing away an oily sheen about 10 miles off the coast.

A report of tarballs on the beach led the news in the local paper last week, though it is uncertain whether the tar came from the spill. "If we were picking a time for something like this to hit, it wouldn't be now," Schroeder said. "Our season just started."

At stake are industries that employ tens of thousands of people and generate billions of dollars in economic activity for coastal areas stretching hundreds of miles. Beyond fishing and tourism, the offshore oil business is likely to feel the effects soon, too, as some exploration halts under a federal moratorium, analysts said, and new safety measures are required.

"It's clearly going to make deep-water exploration more costly," said Edward Morse, a Credit Suisse oil analyst. "My rough estimate is that it will have at most a 10 to 15 percent increase in costs developing crude from deep water."

For gulf regions from Texas to Key West, commercial fishing contributes $1 billion to GDP, tourism and recreation contribute $13 billion, and oil and gas contribute $11 billion, according to figures from Charles Colgan of the National Ocean Economics Program.

Shrimp boats idle

As the slick slides toward Mississippi, Alabama and Florida, the damage could spread.

At the Mariah Jade Shrimp Company in Chauvin, La., Kim and David Chauvin have watched as the closing of about a quarter of the gulf to fishing has made the flow of shellfish to their dock just a trickle. The company has three of its own shrimping vessels, which have been enlisted to help contain the spill.

"Our dock is pretty much closed," said Kim Chauvin, 42. "At this point, we are going to be looking for other jobs. . . . What's really scary is wondering how much marine life will be left when this is all over."